Applied to Leaves 
As far as we know, all regulating compounds are absorbed by leaves and most of them 
are translocated to other parts of plants (43), Absorption and translocation are favored by 
such conditions as relatively high light intensity, high humidity, and moderate tempera- 
tures (10, 12, 20, 27, 33, 38, 58). It has long been known that movement of regulating 
chemicals from the leaves to other parts of the plant is associated with movement of 
photosynthate in the same direction (38, 63). The rate at which regulating compounds are 
absorbed and translocated from the leaves can be accelerated under certain conditions 
by the addition of such additives as surfactants, sugar, and boron (14, 20, 24, 36, 39, 48). 
A few regulating compounds are not readily translocated out of leaves. For example, 
isopropyl-N-phenylcarbamate was not absorbed and translocated in effective amounts 
from leaves of the Wong barley variety (46). 2, 4-dichlorobenzyl nicotinium sulfate, 
a regulator that suppresses growth, was not readily translocated from the leaves of 
bean plants (49). 
The fate of regulating compounds depends to some extent on the stage of maturity 
of the leaves to which they are applied. Experiments with radioactively tagged regulating 
compounds have shown that relatively immature partly expandedleaves may absorb these 
substances, but these young leaves were unable to translocate effective amounts of the 
chemicals to other parts of the plant. In a similar way, relatively old leaves do not 
absorb and translocate regulating compounds to other parts of the plant as effectively 
as do leaves in their prime (42). Metabolism of regulating substances by leaves in these 
different stages of maturation has not been studied. 
Most regulating compounds are moved in both an upward and a downward direction 
after translocation to the stems. The final distribution pattern, however, depends to 
some extent upon the type of regulating chemical used. Some, such as 2-iodo-3-nitro- 
benzoic acid (or its metabolites), accumulated in the tips of bean plants after application 
to the leaves while 2, 4-dichloro-5-iodophenoxyacetic acid (or its metabolites) accumu- 
lated mainly in the lower stem (43). 
Some regulating chemicals move from leaves and accumulate more readily in the 
aboveground parts of the plant than in their roots (20, 41). There is evidence that certain 
regulating chemicals may accumulate in the seeds of plants after application to the 
leaves. For example, a growth-suppressing chemical known as Amo-1618 applied to the 
leaves of bean plants accumulated in the seeds in sufficient amounts to suppress greatly 
the growth of plants that develop from these seeds. The regulator accumulated in the 
seeds either as the compound applied to the plant or as a metabolite capable of inducing 
identical growth responses (35). 
The fate of growth regulators as far as their absorption and translocation is con- 
cerned depends to some extent upon the molecular structure of the compound involved, 
It recently has been possible to accelerate absorption and translocation of some regulating 
chemicals, or of their metabolites, by slightly altering their structural configurations. 
For example, the absorption and translocation of phenylacetic acid, 2,4-dichloro- 
phenylmercaptoacetic acid, isopropyl-N-phenylcarbamate and naphthaleneacetic acid were 
enhanced by modifying the parent compounds to lactic acid derivatives (43, 44). The 
increase due to this change varied from about 30 percent for the mercapto compound to 
600 percent for naphthaleneacetic acid. 
With respect to the metabolism of regulators when applied to the leaves of plants, 
some of these compounds apparently enter the plant, remain, in part at least, essentially 
unchanged as they move from the leaves to other parts. For example, alpha-methoxy- 
phenylacetic acid was absorbed by leaves, and then was translocated to the roots and 
exuded into surrounding aerated water without detectable change (30, 3l, 55). Naphtha- 
leneacetic acid applied to leaves of bean plants grown in light from fluorescent tubes 
was absorbed and translocated to the stems without any detectable change (44). Minute 
amounts of both the methoxy acid and the naphthalene acid reacted with some plant 
182 
